There have conventionally been known hybrid vehicle driving systems which include an internal combustion engine and an electric motor (for example, refer to Patent Document 1).
A vehicle driving system 200 of Patent Document 1 includes, as shown in FIG. 15, a dual-clutch type transmission mechanism which includes, in turn, a first input shaft 202a which is connected to an electric motor 210 and which is selectively connected to an internal combustion engine output shaft 204 by a first engaging and disengaging means 205, a second input shaft 202b which is selectively connected to the internal combustion engine output shaft 204 by a second engaging and disengaging means 206, an output shaft 203 which outputs power to a driven portion, a first gear train including plural gears which are selectively connected to the first input shaft 202a via first synchromesh units 230, 231 which are disposed on the first input shaft 202a, a second gear train including plural gears which are selectively connected to the second input shaft 202b via second synchromesh units 216, 217 which are disposed on the second input shaft 202b, and a third gear train which is disposed on the output shaft 203 and which includes plural gears which mesh with the gears of the first gear train and the gears of the second gear train, and a reverse gear set R, which is selectively connected to the second input shaft 202b via a second synchromesh unit 217, is provided on the second input shaft 202b to which the electric motor 210 is not connected.